Selector and receiver for radio frequency energy



F. A. KOLSTER 1.717.455

SELECTOR AND RECEIVER FOR RADIO FREQUENCY ENERGY June 18, 1929.

Filed July 2, 1923 I N V EN TOR. AA ffo/szem 54:4 ATTORNEYS.

Patented June 18, 1929.

UNITED STATES 1,711,455 PATENT OFFICE.

FREDERICK A. KOLSTER, OF SAN JOSE, CALIFORNIA, ASSIGNOR TO FEDERAL TELE- GRAPH COMPANY, OF SAN FRANCISCO, CALIFORNIA, A CORPORATION OF CALI- FORNIA.

SELECTOR AND RECEIVER FOR RADIO FREQUENCY ENERGY,

Application filed July 2, 1923. Serial No. 648,918.

This invention relates to the art of signaling by the aid of radio frequency currents, and more specifically to a scheme whereby it is possible to select signals of a desired frequency at the receiver. This has been accor n.

plished to a certain extent by tuning the circuits associated with the receiver by the aid of variable capacities or inductances.

It is however, one of the objects of my invention to make it possible to tune such a receiver much more sharply, so that there will be less interference between signals transmitted at different frequencies.

It is another object of my invention to provide a selector unit that may readily be inserted in any one of many types of transmitting or receiving circuits, and that is simple in construction as well as readily adjustable to the desired signaling wave length.

In prior devices, it has been customaryto utilize an apparatus, comprising a plurality of inductively associated windings, the coupling between which may be varied to secure .a high degree of selectivity. The coupled coils for this purpose are interposed between the receit'ing circuit and the detector. In this form of apparatus, the degree of selectivity depends upon the looseness of coupling between the windings, so that in general, the

looser the coupling the sharper the tuning becomes. The great disadvantage of this form of tuning is that high selectivity is obtained at the expense ofdiverting a large part of the energy received in the receiving circuit or generated by the'transmitter, and in order to secure a suflicient volume of sound,

many stages of amplification must be pro vided. Furthermore, the manipulation is rather complex. It is thus another object 40 of my invention to provide a scheme for rendering a signaling circuit highly selective while obviating the need for loose coupling.

I11 this way.. only relatively few stages of audio or radio frequency amplification are necessary to produce the desired intensity of the signal.

My invention may be used equally well' for the reception or transmission oftelegraphic signals as well as of speech, and furthermore it is1 immaterial what type of circuit is uti lize My invention possesses other advantageous.

. features, some of which with the foregoing,

will be set forth at length in the following description, where I shall outline in full these forms of theinvention which I have selected for. illustration in the drawings accompanymg and forming part of the present specification. Although I have shown in the drawings only a few embodiments of my invention, I do not desire to be limited thereto, since the invention as expressed in the claims may be embodied in other forms also.

Referring to the drawings:

Figure 1 is a wiring diagram showing one form of receiving apparatus embodying my invention, in which an antenna is used as an absorbing circuit;

Fig. 2 is a wiring diagram of a modified form of my invention; and

Fig, 3 is a fragmentary wiring diagram showing the-application of my invention to a radio compass.

In the present instance I have shown my invention applied to a receiver utilizing thermionic devices both for amplification and detectmmalthough as. is apparent, other types of devices may be used with my invention. Furthermore in Fig. 1 the absorbing circuit includes an antenna 11, a loading inductor such as a variometer 12, a variable condenser 13, and ground 14., This circuit may be tuned as is usual, to the incoming radio frequency. In Fig. 1, I show two stages of radio frequency amplification, provided by the amplifiers 15 and 16, which are used to amplify the radiofrequency waves before they are detected in the detector tube 17. After detection one or more audio frequency amplifiers such as 18 may be used. The numher of stages'of amplification may of course be varied to suit individual taste or requirement.

Although it is possible to connect the amplifier 15 to the absorbing circuit in a variety ofways, I prefer to use for this purpose a transformer 19, the primary 20 of which may be connected across one of the elements in the absorbing circuit, such' as the condenser13. The terminals of secondary 21, connect respectively to the control electrode 22, usually in the form of a grid, and to the filament 23'adapted to be heated by a battery 24. The variations in the relative potentials of the grid 22 and filament 23, produced by the cause corresponding amplified variations in the output circuit of the tube 15, in a well understood manner. cludes the plate 25, the primary 26 of a transformer 27. a source of potential 28 for maintaining the plate positive with respect to the filan'ient 23; and the filament 23.

It is to be noted that, irrespective of the particular manner of connecting the amplifier 15 to the absorbing circuit, there is a close coupling between them, so that substantially all of the energy received is useful in affecting the amplifier 15. In the present instance the transformer 19 isfor this purpose provided with a magnetic core 29 upon which the primary and secondary windings 20 and 21 are closely wound. In order to provide a path for currents of other than the desired frequency, so that they do not affect the amplifier 15, a device 30 is bridged across the secondary 21. This device is a selector, and includes an inductance 31 and capacity 32 in parallel. This inductance and capacity are so tuned that in parallel they offer a very high impedance only to curreuts'at or near the frequency of the radio signals which are to be received. This may readily be accomplished by so adjusting the inductance 31 and capacity 32 that at this frequency the inductive rcactance is equal to the capacitive reactancc. This adjustment may be accomplished either by varying the condenser alone, or the inductance alone, or by varying both of them. Under such circumstances whatever currentof the tuned frequency may be flowing in the inductance 31 has its exact counterpart in the capacity 32, since these ele ments. have the same E. M. F. impressed across them from the winding 21. Thus so far as the external circuit is concerned, these two currents cancel each other. and none can flow through the'selector, although it may circulate in the closed path formed by the elements 31 and 32.

It is advisable at this stage to discuss more fully the great advantages that arise from connecting the selector 30 in the location shown. It prevents substantial loss of energy at the tuned frequency, and obviates the necessity of a loose coupling between coils 20 and 21 to secure selectivity, since much of the undesired currents flow through the selector 30 and do not affect the amplifier 15. In addition, the circulation of the tuned frequency current in the closed path has a tendency to boost the E. M. F. across the input terminals of the amplifier 15.

I prefer to associate the transformer 19 with the selector 30 as a unit, as by mounting them together in a box or space 33 indicated in dotted lines. In this way it may be shifted at will to any other desirable location. such as I shall now describe. For accomplishing this result in an expeditious manner, I provide terminals 34 and 35 for the selector unit,

This output circuit in-- respects its operation in connection with amplifier 16 is similar to that already discussed. I also indicate, by aid of dotted rectangle 38, that the transformer 27 and selector 36 may be mounted on a common base to form a selector unit.

The detector 17 has its input circuit connected to the secondary 39 of the transformer 40, the primary 41 of which is included in the output circuit of amplifier 16. A selector 42 is connected across this secondary, and operates as described hereinbefore. The detector 17 has a grid condenser 43 and a grid leak resistance It as is common practice. Beyond the detector. one or more audio frequency amplifiers, such as 18 may be provided, any of which may have a selector 45. In this instance howcver the transformer 46 that couples the amplifier 18 to the preceding apparatus is designed for audio frequency. and

furthermore the selector 4-5 is arranged to he anti-resonant at this audio frequency. Finally the translating device 11 such as head phones, is located in the output circuit of the last amplifier. The amplifying arrangement of. course may be multiplied, and each stage may if desired be provided with the antiresonant device.

In Fi 2 as another exam )le I illustrate erably one slightly below and the other:

slightly abovethe radio frequency which it is desired to receive, and furthermore it should be noted that the two inductances 53 and 55 have a common terminal 57 which is conected to one side of the transformer wind ing 50. I

It may be readily demonstrated that the E. M. F. drop across inductor 53 is a maximum for currents at the frequency for which the circuit 53, 54 is tuned, and the same is true-for the E. M. F. drop across the inductor mamas 55. The frequency of reception being intermediate and very. close to the frequencies tuned for in these circuits, will cause a comparatively large E. M. F. to exist across these inductors. On the other hand, this effect rapidly diminishes when currents are imposed upon the circuits which diverge from the two limiting frequencies for which the circuits are tuned. In this way therefore there is a selective action similar to that already discussed in connection with Fig. 1. The selector 48 and transformer 51 may be mounted on a common support 58.

The drop across the inductors 53and 5 may be used to affect the input .circuits of a pair of amplifier tubes, or of a double tube 49. For this purpose the grids 59 and 60 are connected to the ends of induct'ors53 and 55 respectively, and the filament 61 common to both of the tube elements, is connected to the terminal 57 of the inductors. Each output circuit includes a transformer primary section 62 or 63, as well as the battery 64. The effects of sections 62 and 63 are made additive as indicated by arrows 65 and 66, on the secondary winding 67 of the transforn'icr 68. From this secondary, the selector arrangement may again-berepeated as often as desired, either of the two-forms of selectors being adaptable. I show a detector 69 connected to the secondary 67, across which a selector 7 0 of the first type is connected. The output circuit of the tube 69 includes the telephone 71 or other form of-translating device.

It is not at all necessary that the invention be utilized with any particular form of absorbing cirduit, such as illustrated in Figs. 1 and 2. For example its use with a radio compass has particular advantages, since it augments the selective properties of the compass verymaterially. An arrangement is shown in the fragmentary Fig. 3 illustrating a radio compass circuit, for example such as described and claimed in a patent granted Feb. 27, 1923, in my name, having number 1,447,165, and entitled Radio method and apparatus; Broadly such an arrangement,

includes a tuned closed circuit in the form of, a rotatable loop 72 and a variable condenser 73, as well as a ground conncction74." This ground connection, in order to secure unidirectional eflects as explained in my prior patent, is nnsymmetricallyconnected to the loop circuit as bythe aid of oppositely variable condensers 76 and 77. The loop 72 serves not only to absorb radio energy .directly, but also as an elevated conductor for an open circuit receiver of which the ground forms the counterpoise. There is an energy interchange between the open and closed absorption circuits dependent upon the extent of unbalancing of condensers 76 and 77, and it is this interchange that produces the unidirectional efiect, all as explained in my prior patent.

The amplifier or detector circuit is associatcd with the radio compass by connecting across the coil or loop 72. From this point on the circuit may take theform of either Fig. 1 or Fig. 2, and includes one or more selectors 78, each connected in shunt to the secondary of an amplifier transformer 79, and also to the input circuit of a detector or amplifier tube, as explained hereinbefore.

I claim:

1. In a selector, a closely coupled transformer adapted to be interposed between a thermionic device and an incoming circuit for the device, said transformer having incoming and outgoing terminals, and a frequency selector connected to the outgoing terminals of the transformer, said selector comprising an inductance shunted by a capacity and being arranged to by pass energy without materially affecting the input circuit of the thermionic device except when the signaling currents have a frequency in the neighborhood of that which it is desired to use.

2. In combination, a detector having an detector except when the currents have a frequency in the neighborhood of that which it is desired to use, one of said reactances being inductive and the other of said reactances' being capacitative. I

3. In combination, an amplifier having an input and an output circuit, inductively coupled means connected to each of said circuits and a frequency selector connected directly across the input circuit, comprising aplurality of reaetances connected in parallel and arranged to by-pass energy without materially affecting the input circuit of the amplifier except when the currents have a frequency in the neighborhood of-that which it is desired to use, one of said reacta-nces being inductive and the other of said reactances bcing capacitative.

4. In combination, a device for modifying high frequency energy, having an input and an output'circuit arranged to be inductively coupled with independent circuits, and a frequency selector for confining the frequency of operation of the device .within definite limits, connected directly across the input circuit thereof, said selector comprising solely an inductor and a capacity in parallel, said elements being adjustable to provide a maximum impedance to the passage of a current of the desired frequency of operation.

5. In combination, a high frequency closely coupled transformer having a winding adapted to be connected to the input circuit of a connected inductive and capacitative react- 13 times for confining the frequency of operation within definite limits, connected across the winding.

6. In combination, a high frequency closely.

coupled transformer having primary and secondary windings with its secondary winding adapted to be connected to the input circuit of a device for modifying high frequency energy, and a frequency selector for confining thefrequency of operation within definite limits, connected across the Winding, said selector comprising solely an inductor and a capacity in parallel, and adjustable to provide a maximum impedance to the passage.

of a current of the desired frequency of operation. 7. In a radio receiving system, an absorbing circuit, one or more radio frequency thermionic amplifiers having input and output circuits, transformers closely coupling the output circuit of each amplifier to the input circuit of the succeeding amplifier, and

to the absorbing circuit, a detector tube having an input and an output circuit, a trans former closely coupling the detector tube to the last amplifier, one or more audio frequency amplifiers, transformers closely coupling said last mentioned amplifiers in succcssion, a transformer closely coupling the first of the series to the output circuit of the detector tube, and frequency selectors connected across at least some of the input circuits of the various tubes, for confining the operation of the system to or near a desired frequency. i

.8. In a radio receiving. system, an absorbing circuit, one or more radio frequency ther mionic amplifiers having input and: output circuits, transformers closely coupling the output circuit of each amplifier to the input circuit of the succeeding amplifier, and to the absorbing circuit, a detector tube having aninput and an output circuit, a transformer closely coupling the detector tube to the last amplifier, one or more audio frequency am-- plifiers, transformers closely coupling said last mentioned amplifiers in succession, a

transformer closely coupling the first of the series to the output circuit of the detector tube, and frequency selectors connected across the input circuits of both said radio and audio frequency amplifiers, for confining the operation of the system to or near a desired frequency, each of the frequency selectors comprising an inductor and a capacltance in A parallel, adjusted to offer substantially a maximum impedance to currents of the desired frequency of operation.

rality of thermionic devices having inputand output circuits, associated with the absorbing circuit, transformers closely coupling these devices together, and to the circuit, and frequency selectors constituted by inductive and capacitative reactances connected across each of the input circuits for confining the operation of the system to or near a desired frequency.

11. In a receiving system, a pair ofinductively coupled tubes, whereby one tube may pass an amplified signal impulse to the other, and means forming a circuit in parallel to the tubes and between them, said circuit being constitutedby an inductance shunted by a capacity arranged to have a maximum impedance only for currents of the frequency of the signaling currents, said'inductance and capacity being proportional to the coupling circuit for selectively adjusting each succeeding tube circuit in the receiving'system for the reception of a particular frequency to the exclusion of other frequencies. I v

12. An amplification system. comprising a plurality of electron tubes each having grid,

filament and plate electrodes, input circuits interconnecting said grid and filament electrodes, output circuits interconnecting said plate and filament electrodes, a transformer having primary and secondary windings closely coupling the input and output cir-;

cuits of an adjacent tube, a' divided circuit bridged across said secondary windings and across the filament and grid electrodes of said input circuit including inductive and capacitative reactances connected in parallel, said reactances being adjusted to substantially the same value for a selected frequency for offering a high impedance to currents at or near the signaling frequency selected to be received.

In testimony whereof, I have hereunto set my hand. c

FIEDERICK A. KOLSTER. 

